Stop pinning Go to patch versions, use stable in CI (#1137)

<!-- Provide a brief summary of your changes -->

## Motivation and Context
<!-- Why is this change needed? What problem does it solve? -->
We keep bumping `go 1.26.x` across the repo every time a new Go patch
drops
## How Has This Been Tested?
<!-- Have you tested this in a real application? Which scenarios were
tested? -->
- **`go.mod` / `deploy/go.mod`**: `go 1.25.8` → `go 1.26` (minor only —
"this module needs Go 1.26")
- **All CI workflows**: `go-version-file: 'go.mod'` → `go-version:
'stable'` — CI always uses the latest stable Go, no more
  bump PRs
- **govulncheck**: removed hardcoded `go-version-input: '1.26.1'` →
`go-version-input: 'stable'`
## Breaking Changes
<!-- Will users need to update their code or configurations? -->

## Types of changes
<!-- What types of changes does your code introduce? Put an `x` in all
the boxes that apply: -->
- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)
- [ ] Documentation update

## Checklist
<!-- Go over all the following points, and put an `x` in all the boxes
that apply. -->
- [ ] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [ ] My code follows the repository's style guidelines
- [ ] New and existing tests pass locally
- [ ] I have added appropriate error handling
- [ ] I have added or updated documentation as needed

## Additional context
<!-- Add any other context, implementation notes, or design decisions
-->

Signed-off-by: Radoslav Dimitrov <radoslav@stacklok.com>

.github/workflows/ci.yml

@@ -21,13 +21,13 @@ jobs:
     - name: Set up Go
       uses: actions/setup-go@4a3601121dd01d1626a1e23e37211e3254c1c06c
       with:
-        go-version-file: 'go.mod'
+        go-version: 'stable'
         cache: true
 
     - name: Run lint
       uses: golangci/golangci-lint-action@1e7e51e771db61008b38414a730f564565cf7c20
       with:
-        version: v2.4.0
+        version: v2.11.4
 
     - name: Validate schemas and examples
       run: make validate
@@ -38,9 +38,7 @@ jobs:
     - name: Run govulncheck
       uses: golang/govulncheck-action@v1
       with:
-        # Use Go 1.26.1 to pick up crypto/x509 vulnerability fixes (GO-2026-4600, GO-2026-4599).
-        # go.mod stays at go 1.25.8 for golangci-lint compatibility until it supports Go 1.26.
-        go-version-input: '1.26.1'
+        go-version-input: 'stable'
         go-package: ./...
         repo-checkout: false
 
@@ -55,7 +53,7 @@ jobs:
     - name: Set up Go
       uses: actions/setup-go@4a3601121dd01d1626a1e23e37211e3254c1c06c
       with:
-        go-version-file: 'go.mod'
+        go-version: 'stable'
         cache: true
 
     - name: Set up ko

.github/workflows/deploy-production.yml

@@ -28,7 +28,7 @@ jobs:
       - name: Setup Go
         uses: actions/setup-go@4a3601121dd01d1626a1e23e37211e3254c1c06c
         with:
-          go-version-file: 'deploy/go.mod'
+          go-version: 'stable'
           cache: true
 
       - name: Setup Pulumi

.github/workflows/deploy-staging.yml

@@ -27,7 +27,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@4a3601121dd01d1626a1e23e37211e3254c1c06c
         with:
-          go-version-file: 'go.mod'
+          go-version: 'stable'
           cache: true
 
       - name: Set up ko
@@ -75,7 +75,7 @@ jobs:
       - name: Setup Go
         uses: actions/setup-go@4a3601121dd01d1626a1e23e37211e3254c1c06c
         with:
-          go-version-file: 'deploy/go.mod'
+          go-version: 'stable'
           cache: true
 
       - name: Setup Pulumi

.github/workflows/release.yml

@@ -21,7 +21,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@4a3601121dd01d1626a1e23e37211e3254c1c06c
         with:
-          go-version-file: 'go.mod'
+          go-version: 'stable'
           cache: true
 
       - name: Install cosign
@@ -50,7 +50,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@4a3601121dd01d1626a1e23e37211e3254c1c06c
         with:
-          go-version-file: 'go.mod'
+          go-version: 'stable'
           cache: true
 
       - name: Set up ko